1. Field of the Invention
The present invention relates to a laminated varistor, and more particularly, it relates to structure in a laminated varistor for preventing decomposition of internal electrodes.
2. Description of the Background Art
A varistor is a resistor element whose resistance value nonlinearly changes in response to applied voltage.
FIG. 17 shows a conventional varistor 1 of a laminated type provided in the form of a rectangular parallelepiped. The laminated varistor 1 shown in FIG. 17 is substantially identical in structure to a laminated varistor which is disclosed in U.S. Pat. No. 4,290,041.
Referring to FIG. 17, the laminated varistor 1 comprises a sintered body 5, which is obtained by alternately stacking ceramic layers 2 and internal electrodes 3 or 4 and integrally sintering the same. First and second external electrodes 8 and 9 of metal are provided on first and second opposite end surfaces 6 and 7 of the sintered body 5. The internal electrodes 3 of a first group have end portions 10 reaching the first end surface 6, to be electrically connected to the first external electrode 8. The internal electrodes 4 of a second group, which are arranged alternately with the internal electrodes 3 of the first group, have end portions 11 reaching the second end surface 7, to be connected to the second external electrode 9.
This laminated varistor 1, and more specifically the sintered body 5, has such structure that the respective end portions 10 and 11 of the internal electrodes 3 and 4 are exposed toward the exterior of the sintered body 5. Therefore, when the sintered body 5 is placed in a humid atmosphere, the exposed portions of the internal electrodes 3 and 4 are easily decomposed. Further, when the external electrodes 8 and 9 are formed by plating, the plating solution easily permeates the sintered body 5 from the exposed portions of the internal electrodes 3 and 4. Consequently, characteristics of the laminated varistor 1 are deteriorated.